In general, the present invention relates to improvements in weapons systems and in particular to devices and methods for predicting parameters useful for determining the aim of projectiles. It is especially, although not exclusively, suited to applications concerning the aiming of a shell fired from a gun. The invention extends to prediction and aiming methods and devices per se and to weapons systems incorporating such devices. One important aspect of the invention entails prediction of muzzle velocity.
The accuracy of indirect-fire weapons is dependent on a multitude of factors. For a long time, one major cause of inaccuracy has been unpredictable variation in muzzle velocity. Ideally, ignoring environmental factors such as wind, for a given combination of barrel type, charge and projectile, the muzzle velocity would be substantially constant. However, in reality it varies in dependence on a number of effects, such as barrel temperature, barrel wear and the inevitable small variations in the manufacture of barrels and shells of nominally the same type.
Up to now, the common practice for an initial firing has been to set the quadrant elevation (hereinafter simply called elevation) for a gun laying system by referring to "firing tables." Subsequent adjustments for further firings are then made, again with the aid of these tables. The firing tables are produced by calibration firings undertaken for a given barrel type under various conditions. Current calibration practice involves formulation of a Reduced muzzle Velocity (RMV) which is an actual velocity corrected to a nominal standard projectile mass and charge temperature.
However, even if these firing tables are regularly updated based on calibration firings of further barrels manufactured to the same specification, they can never take account of all the variations in muzzle velocity which are encountered with real-life firings, whether arising from known or unknown sources. This conventional practice based on use of firing tables has inherent inaccuracies for reasons which include the following:
a) A single calibration value cannot be applied to all guns of a type. Analysis shows that individual barrels have consistent characteristics which are significant to muzzle velocity prediction but which are unique to the barrel.
b) A single calibration value cannot be applied to a single barrel even for the duration of a series of firings.
c) Significantly, the first few firings of a series show significant variations from the calibrated value.
With reference to FIG. 1 of the accompanying drawings, here it is convenient to define the following expressions pertaining to gun control:
Series. A series of firings is defined to start whenever:
a different propellant charge is used to fire the projectile than the charge used to fire the previous projectile;
gun maintenance of any form has occurred; or
the barrel is "cold," i.e., a significant period has elapsed since the previous firing.
Point of Aim (POA). This is the point where it is desired for the shells to fall. Normally there is a target present at this location.
Mean Point of Impact (MPI). This point is the centroid of the points where the projectiles actually land. It is displaced from the POA because of a number of factors, including differences between the actual muzzle velocity of the projectiles fired and the muzzle velocity used in aiming calculations.
Accuracy. The accuracy is defined as the displacement between the POA and the MPI.
Precision. Precision is defined as the dispersion of shell impact points around the MPI.
It is an object of the present invention to provide increased accuracy, i.e. to decrease the distance between the Point of Aim and the Mean Point of Impact. It is also an object of the invention to improve the Precision such that the dispersion of the shells, around the MPI, is smaller.